Re: [RFC 1/1] drm: allow to use mmuless SoC

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Benjamin,

On Wednesday 30 Nov 2016 16:34:37 Benjamin Gaignard wrote:
> 2016-11-30 16:19 GMT+01:00 Laurent Pinchart:
> > On Wednesday 30 Nov 2016 16:08:23 Benjamin Gaignard wrote:
> >> 2016-11-30 14:52 GMT+01:00 Daniel Vetter <daniel@ffwll.ch>:
> >>> On Wed, Nov 30, 2016 at 12:21:24PM +0100, Benjamin Gaignard wrote:
> >>>> Some platforms without MMU have display drivers where a drm/kms driver
> >>>> could be implemented.
> >>>> Before doing such kind of thing drm/kms must allow to use mmuless
> >>>> devices.
> >>>> This patch proposes to remove MMU configuration flag and add some
> >>>> cma helpers functions to help implementing mmuless display driver
> >>>> 
> >>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> >>>> ---
> >>>> 
> >>>>  drivers/gpu/drm/Kconfig              |  4 +--
> >>>>  drivers/gpu/drm/drm_fb_cma_helper.c  | 20 ++++++++++++
> >>>>  drivers/gpu/drm/drm_gem_cma_helper.c | 62 +++++++++++++++++++++++++++
> > 
> > [snip]
> > 
> >>> drm_vm.c is a legacy horror show. Instead of hacking even more garbage
> >>> into this, can't we just not compile this for MMU-less platforms? A
> >>> bunch of stubs in drm_internal.h is all that should be needed for this,
> >>> since on MMU-less you should never be able to enable one of the legacy
> >>> drivers which need the exported symbols from this file.
> >> 
> >> Following your advice I have removed drm_vm.c from the build if
> >> CONFIG_MMU is not set
> > 
> > How about only including it if !DRM_LEGACY && !DRM_NOUVEAU ?
> 
> I don't understand the link between !DRM_LEGACY && !DRM_NOUVEAU and MMU...
> 
> By chance would you mean including only if DRM_LEGACY && DRM_NOUVEAU ?

I meant excluding it if !DRM_LEGACY && !DRM_NOUVEAU, sorry, so including it if 
DRM_LEGACY || DRM_NOUVEAU.

(Probably out of scope for this patch series, but why do we need it in nouveau 
?)

> >> I only had to stub drm_legacy_vma_flush() to compile.
> >> I will include that in v3

-- 
Regards,

Laurent Pinchart

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